Visible-light-assisted electrocatalytic oxidation of methanol using reduced graphene oxide modified Pt nanoflowers-TiO2 nanotube arrays

Graphene and Perovskite-Based Nanocomposite for Both Electrochemical and Gas Sensor Applications: An Overview

Perovskite and graphene-based nanocomposites have attracted much attention and been proven as promising candidates for both gas (H₂S and NH₃) and electrochemical (H₂O₂, CH₃OH and glucose) sensor applications. In this review, the development of portable sensor devices on the sensitivity, selectivity, cost effectiveness, and electrode stability of chemical and electrochemical applications is summarized. The authors are mainly focused on the common analytes in gas sensors such as hydrogen sulfide, ammonia, and electrochemical sensors including non-enzymatic glucose, hydrazine, dopamine, and hydrogen peroxide. Finally, the article also addressed the stability of composite performance and outlined recent strategies for future sensor perspectives.

Multi-Leg TiO2 Nanotube Photoelectrodes Modified by Platinized Cyanographene with Enhanced Photoelectrochemical Performance

Highly ordered multi-leg TiO2 nanotubes (MLTNTs) functionalized with platinized cyanographene are proposed as a hybrid photoelectrode for enhanced photoelectrochemical water splitting. The platinized cyanographene and cyanographene/MLTNTs composite yielded photocurrent densities 1.66 and 1.25 times higher than those of the pristine MLTNTs nanotubes, respectively. Open circuit VOC decay (VOCD), electrochemical impedance spectroscopy (EIS), and intensity-modulated photocurrent spectroscopy (IMPS) analyses were performed to study the recombination rate, charge transfer characteristics, and transfer time of photogenerated electrons, respectively. According to the VOCD and IMPS results, the addition of (platinized) cynographene decreased the recombination rate and the transfer time of photogenerated electrons by one order of magnitude. Furthermore, EIS results showed that the (platinized) cyanographene MLTNTs composite has the lowest charge transfer resistance and therefore the highest photoelectrochemical performance.

Conformal Solution Deposition of Pt-Pd Titania Nanocomposite Coatings for Light-Assisted Formic Acid Electro-Oxidation

Many nanofabrication processes require sophisticated equipment, elevated temperature, vacuum or specific atmospheric conditions, templates, and exotic chemicals, which severely hamper their implementation in real-world applications. In this study, we outline a fully wet-chemical procedure for equipping a 3D carbon felt (CF) substrate with a multifunctional, titania nanospike-supported Pt-Pd nanoparticle (Pt-Pd-TiO₂@CF) layer in a facile and scalable manner. The nanostructure, composition, chemical speciation, and formation of the material was meticulously investigated, evidencing the conformal coating of the substrate with a roughened layer of nanocrystalline rutile spikes by chemical bath deposition from Ti³⁺ solutions. The spikes are densely covered by bimetallic nanoparticles of 4.4 ± 1.1 nm in size, which were produced by autocatalytic Pt deposition onto Pd seeds introduced by Sn²⁺ ionic layer adsorption and reaction. The as-synthesized nanocomposite was applied to the (photo)electro-oxidation of formic acid (FA), exhibiting a superior performance compared to Pt-plated, Pd-seeded CF (Pt-Pd@CF) and commercial Pt-C, indicating the promoting electrocatalytic role of the TiO₂ support. Upon UV-Vis illumination, the performance of the Pt-Pd-TiO₂@CF electrode is remarkably increased (22-fold), generating a current density of 110 mA cm^-2, distinctly outperforming titania-free Pt-Pd@CF (5 mA cm^-2) and commercial Pt-C (6 mA cm^-2) reference catalysts. In addition, the Pt-Pd-TiO₂@CF showed a much better stability, characterized by a very high poisoning tolerance for in situ-generated CO intermediates, whose formation is hindered in the presence of TiO₂. This overall performance boost is attributed to a dual enhancement mechanism (∼30% electrocatalytic and ∼70% photoelectrocatalytic). The photogenerated electrons from the TiO₂ conduction band enrich the electron density of the Pt nanoparticles, promoting the generation of active oxygen species on their surfaces from adsorbed oxygen and water molecules, which facilitate the direct FA electro-oxidation into CO₂.

Bacteria-Assisted Synthesis of Nanosheet-Assembled TiO2 Hierarchical Architectures for Constructing TiO2-Based Composites for Photocatalytic and Electrocatalytic Applications

Synthesis and application of three-dimensional TiO₂ hierarchical architectures are one of the major priorities in the research and development of TiO₂ catalysts. Using bacteria as a template and a reactor, a bioinspired strategy was developed in the present study to synthesize nanosheet-assembled TiO₂ hierarchical architectures (N-TiO₂-HA) and relative composites for photocatalytic and electrocatalytic applications. In the first part of this work, three kinds of bacteria were used for the synthesis of N-TiO₂-HA with satisfactory monodispersity, and the growth mechanism was investigated. In the second part, porous TiO₂ hollow spheres (P-TiO₂-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in air, were incorporated with MIL-101(Fe) to improve the visible-light photocatalytic efficiency. The results of the photo-Fenton-assisted degradation of rhodamine B and ciprofloxacin indicate that the synthesized composites have excellent visible-light photocatalytic activity. In the third part, the nanosheet-assembled TiO₂-carbon hollow spheres (N-TiO₂-C-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in argon atmosphere, were electrodeposited with Pt for electrocatalytic oxidation of methanol. The electrochemical measurements show that Pt-deposited N-TiO₂-C-HS have better electrocatalytic activity, stability, and tolerance to CO poisoning than commercial Pt/C catalysts.

Regulating effect of heterojunctions on electrocatalytic oxidation of methanol for Pt/WO3-NaTaO3 catalysts

Pt/WO₃-NaTaO₃ composite catalysts for different W/Ta molar ratios were obtained via a facile hydrothermal method.

Surface-modified Pt1Ni1–Ni(OH)2 nanoparticles with abundant Pt–Ni(OH)2 interfaces enhance electrocatalytic properties

Pt₁Ni₁–Ni(OH)₂ NPs with abundant Pt–Ni(OH)₂ interfaces exhibit a rather high activity and stability for the MOR in alkaline electrolytes.

Enhanced Photoinduced Electrocatalytic Oxidation of Methanol Using Pt Nanoparticle-Decorated TiO2-Polyaniline Ternary Nanofibers

Herein, perylene-3,4,9,10-tetracarboxylic acid-doped polyaniline (PTP) nanofibers with/without photoreactive anatase TiO₂ (TiO₂-PTP and PTP, respectively) have been successively synthesized and subsequently decorated by Pt nanoparticles (Pt NPs) to prepare Pt-PTP and Pt-TiO₂-PTP composites. High-resolution transmission electron microscopy confirms the presence of ∼3 nm spherical-shaped Pt NPs on both the composites along with TiO₂ on Pt-TiO₂-PTP. Pt loading on the composites is deliberately kept similar to compare the methanol electro-oxidation in the two composites. The Pt nanocomposites along with the precursor polyanilines are characterized by optical characterization, X-ray diffraction study, X-ray fluorescence spectroscopy, and Raman spectroscopy. The ternary composite-modified (Pt-TiO₂-PTP) electrode demonstrates high electrocatalytic performance for methanol oxidation reaction in acid medium than Pt-PTP and Pt-TiO₂. The higher electrochemical surface area (1.7 times), high forward/backward current ratio, and the higher CO tolerance ability for Pt-TiO₂-PTP make it a superior catalyst for methanol oxidation reaction in the electrochemical process than Pt-PTP. Moreover, the catalytic activity of Pt-TiO₂-PTP is further enhanced significantly with light irradiation. The cooperative effects of photo- and electrocatalysis on methanol oxidation reaction in Pt-TiO₂-PTP enhance the methanol oxidation catalytic activity approximately 1.3 times higher in light illumination than in dark. Therefore, the present work will be proficient to get a light-assisted sustainable approach for developing the methanol oxidation reaction activity of Pt NP-containing catalysts in direct methanol fuel cells.

2D/2D Heterostructured CdS/WS2 with Efficient Charge Separation Improving H2 Evolution under Visible Light Irradiation

Efficient water splitting for H₂ evolution under visible light irradiation has attracted more attention for solving the global environmental and energy issues, but it is still a major challenge to develop an earth-abundant and efficient photocatalyst. Herein, we report two-dimensional (2D)/2D heterostructured CdS/WS₂ (CdS/WS₂), composed of nanosheet CdS (CdS) and nanosheet WS₂ (WS₂), as an efficient photocatalyst for H₂ evolution. As a noble metal-free visible light-driven catalyst for H₂ evolution, CdS/WS₂ with 10 wt % WS₂ exhibited the largest H₂ evolution rate of 14.1 mmol g^-1 h^-1 under visible light irradiation to be 8 times larger than that of pure CdS. The lifetime and dynamics of photogenerated electrons were evaluated by femtosecond time-resolved diffuse reflectance spectroscopy, indicating that WS₂ works as an electron-trapping site and a cocatalyst to cause H₂ evolution under visible light irradiation. This work suggests that CdS/WS₂ has great potential as a low-cost and highly efficient photocatalyst for water splitting.

Recent developments of nano-structured materials as the catalysts for oxygen reduction reaction

Developments of high efficient materials for electrocatalyst are significant topics of numerous researches since a few decades. Recent global interests related with energy conversion and storage lead to the expansion of efforts to find cost-effective catalysts that can substitute conventional catalytic materials. Especially, in the field of fuel cell, novel materials for oxygen reduction reaction (ORR) have been noticed to overcome disadvantages of conventional platinum-based catalysts. Various approaching methods have been attempted to achieve low cost and high electrochemical activity comparable with Pt-based catalysts, including reducing Pt consumption by the formation of hybrid materials, Pt-based alloys, and not-Pt metal or carbon based materials. To enhance catalytic performance and stability, numerous methods such as structural modifications and complex formations with other functional materials are proposed, and they are basically based on well-defined and well-ordered catalytic active sites by exquisite control at nanoscale. In this review, we highlight the development of nano-structured catalytic materials for ORR based on recent findings, and discuss about an outlook for the direction of future researches.

Hierarchical TiO2 nanowire/microflower photoanode modified with Au nanoparticles for efficient photoelectrochemical water splitting

The 3D architecture of H-TiO₂ and incorporation of Au NPs contribute to the excellent PEC performance of Au/H-TiO₂-based photoanodes.

Broadening the sunlight response region with carbon dot sensitized TiO2 as a support for a Pt catalyst in the methanol oxidation reaction

Carbon dots with upconversion properties harness unused visible light and act as sensitizers for a TiO₂ supported Pt catalyst in MOR.

Graphene-based materials supported advanced oxidation processes for water and wastewater treatment: a review

Advanced oxidation processes (AOPs) received much attention in the field of water and wastewater treatment due to its ability to mineralize persistent organic pollutants from water medium. The addition of graphene-based materials increased the efficiency of all AOPs significantly. The present review analyzes the performance of graphene-based materials that supported AOPs in detail. Recent developments in this field are highlighted. A special focus has been awarded for the performance enhancement mechanism of AOPs in the presence of graphene-based materials.

Design and Fabrication of Highly Reducible PtCo Particles Supported on Graphene-Coated ZnO

Cobalt particles dispersed on an oxide support form the basis of many important heterogeneous catalysts. Strong interactions between cobalt and the support may lead to irreducible cobalt oxide formation, which is detrimental for the catalytic performance. Therefore, several strategies have been proposed to enhance cobalt reducibility, such as alloying with Pt or utilization of nonoxide supports. In this work, we fabricate bimetallic PtCo supported on graphene-coated ZnO with enhanced cobalt reducibility. By employing a model/planar catalyst formulation, we show that the surface reduction of cobalt oxide is substantially enhanced by the presence of the graphene support as compared to bare ZnO. Stimulated by these findings, we synthesized a realistic powder catalyst consisting of PtCo particles grafted on graphene-coated ZnO support. We found that the addition of graphene coating enhances the surface reducibility of cobalt, fully supporting the results obtained on the model system. Our study demonstrates that realistic catalysts with designed properties can be developed on the basis of insights gained from model catalytic formulation.

Phase Effect of NixPy Hybridized with g-C3N4 for Photocatalytic Hydrogen Generation

The use of noble metal-free nickel phosphides (Ni_xP_y) as suitable cocatalysts in photocatalytic hydrogen (H₂) generation has gained a lot of interest. In this paper, for the first time, three different crystalline phases of nickel phosphides, Ni₂P, Ni₁₂P₅, and Ni₃P, were synthesized and then hybridized with g-C₃N₄ to investigate the phase effect of Ni_xP_y on photocatalytic H₂ generation. It has been found that all three phases of Ni_xP_y work as effective cocatalysts for the enhancement of visible light H₂ generation with g-C₃N₄. The effective charge transfer between g-C₃N₄ and Ni_xP_y, demonstrated by photoelectrochemical properties, photoluminescence, and time-resolved diffused reflectance, contributes to the enhanced photocatalytic H₂ generation performance. Interestingly, Ni₂P/g-C₃N₄ showed the highest photocatalytic activity among the three Ni_xP_y/g-C₃N₄. Ni_xP_y with a higher ratio of phosphorus (Ni₂P) can accelerate charge transfer and provide more Ni-P bonds, leading to a preferable H₂ generation performance.

Facile synthesis of Pt nanoparticles supported on anatase TiO2 nanotubes with good photo-electrocatalysis performance for methanol

A Pt/TNTs/C catalyst showed enhanced MOR performance under the light illumination.

A silicon photoanode for efficient ethanol oxidation under alkaline conditions

A Pt/ZrO₂/n-Si electrode has been employed as the anode for the EOR, exhibiting improved EOR activity and durability under solar illumination.

Enhanced photoelectrocatalytic degradation of ammonia by in situ photoelectrogenerated active chlorine on TiO2 nanotube electrodes

TiO₂ nanotube (TiNT) electrodes anodized in fluorinated organic solutions were successfully prepared on Ti sheets. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were performed to characterize the TiNT electrodes. The linear voltammetry results under irradiation showed that the TiNT electrode annealed at 450°C presented the highest photoelectrochemical activity. By combining photocatalytic with electrochemical process, a significantly synergetic effect on ammonia degradation was observed with Na₂SO₄ as supporting electrolyte at pH10.7. Furthermore, the photoelectrocatalytic efficiency on the ammonia degradation was greatly enhanced in presence of chloride ions without the limitation of pH. The degradation rate was improved by 14.8 times reaching 4.98×10^-2min^-1 at pH10.7 and a faster degradation rate of 6.34×10^-2min^-1 was obtained at pH3.01. The in situ photoelectrocatalytic generated active chlorine was proposed to be responsible for the improved efficiency. On the other hand, an enhanced degradation of ammonia using TiNT electrode fabricated in fluorinated organic solution was also confirmed compared to TiNT electrode anodized in fluorinated water solution and TiO₂ film electrode fabricated by sol-gel method. Finally, the effect of chloride concentration was also discussed.

High Efficiency Photoelectrocatalytic Methanol Oxidation on CdS Quantum Dots Sensitized Pt Electrode

A cadmium sulfide quantum dots sensitized Pt (Pt-CdS) composite was synthesized using a solvothermal method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. The catalytic properties of the as-prepared electrode for methanol oxidation were evaluated by cyclic voltammetry (CV), chronoamperometry, electrochemical impedance spectrum (EIS) and photocurrent responses. The as-prepared Pt-CdS electrode displayed a significant enhancement in the electrocatalytic activity and stability for methanol oxidation in the presence of visible light irradiation. The synergistic effect of both the electro- and photocatalytic reaction contributes to this enhanced catalytic performance. Our result suggests a new paradigm to construct photoelectrocatalysts with high performance and good stability for direct methanol fuel cells with the assistance of visible-light illumination.

Enhanced visible light driven photoelectrocatalytic oxidation of ethanol at reduced graphene oxide/CdS nanowires decorated with Pt nanoparticles

A ternary rGO/CdS NWs/Pt NPs nanocomposite is successfully synthesized via a template-free route and its application for electrocatalytic and photoelectrocatalytic oxidation of ethanol was developed.

Visible light assisted electro–photo synergistic catalysis of heterostructured Pd–Ag NPs/graphene for methanol oxidation

Heterostructured Pd-Ag/GNs catalytic performances for MOR are significantly improved by visible light irradiation: (a) without irradiation, (b) under irradiation.

Synthesis of Pt3Ni microspheres with high performance for rapid degradation of organic dyes

In this study, Pt3Ni microspheres consisted of nanoparticles were synthesized without addition of surfactants via the solvothermal route. The obtained sample was characterized by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscopy (FESEM). Furthermore, the catalytic performance of as-synthesized Pt3Ni microspheres was evaluated on the degradation of different organic dyes (methylene blue, methyl orange, Congo red, and rhodamine B). The results show that different dyes were rapidly decomposed by Pt3Ni microspheres in different pathways. Among different dyes, the formation and further degradation of the intermediates was observed during the degradation of methylene blue and methyl orange, suggesting the indirect degradation process of these dyes. This study provides not only a promising catalyst for the removal of organic contaminants for environment remediation, but also new insights for Pt3Ni alloy as a high-performance catalyst in organic synthesis.

Highly Dispersed Ultrafine Pt Nanoparticles on Reduced Graphene Oxide Nanosheets: In Situ Sacrificial Template Synthesis and Superior Electrocatalytic Performance for Methanol Oxidation

We report a simple and environmentally friendly route to prepare platinum/reduced graphene oxide (Pt/rGO) nanocomposites (NCs) with highly reactive MnOx colloids as reducing agents and sacrificial templates. The colloids are obtained by laser ablation of a metallic Mn target in graphene oxide (GO)-containing solution. Structural and morphological investigations of the as-prepared NCs revealed that ultrafine Pt nanoparticles (NPs) with an average size of 1.8 (±0.6) nm are uniformly dispersed on the surfaces of rGO nanosheets. Compared with commercial Pt/C catalysts, Pt/rGO NCs with highly electrochemically active surface areas show remarkably improved catalytic activity and durability toward methanol oxidation. All of these superior characteristics can be attributed to the small particle size and uniform distribution of the Pt NPs, as well as the excellent electrical conductivity and stability of the rGO catalyst support. These findings suggest that Pt/rGO electrocatalysts are promising candidate materials for practical use in fuel cells.

High performance of electrocatalytic oxidation and determination of hydrazine based on Pt nanoparticles/TiO2 nanosheets

In this work, highly dispersed Pt nanoparticles (PtNPs) were deposited on the surface of the TiO2 nanosheets (TiO2NSs) by the photodeposition method in the presence of methanol as holes scavengers. The results indicated that PtNPs were distributed on TiO2NSs successfully with the diameter of ca. 5-9 nm. The electrochemical experiments such as electrochemical impedance spectroscopy and cyclic voltammetry were used to study the electrochemical properties of the PtNPs/TiO2NSs modified glassy carbon electrode (GCE). The as-prepared PtNPs/TiO2NSs/GCE presents excellent electrocatalytic activity for hydrazine. The sensor can be used to determine hydrazine at low potential with a wide linear range, high sensitivity, and fast response time. Moreover, the sensor exhibits good selectivity and reproducibility. In addition, the recoveries were 100.1-105.3% for hydrazine in the tap water, indicating the PtNPs/TiO2NSs/GCE should be a promising sensor for the determination of hydrazine in real samples.

Engineering noble metal nanomaterials for environmental applications

Besides being valuable assets in our daily lives, noble metals (namely, gold, silver, and platinum) also feature many intriguing physical and chemical properties when their sizes are reduced to the nano- or even subnano-scale; such assets may significantly increase the values of the noble metals as functional materials for tackling important societal issues related to human health and the environment. Among which, designing/engineering of noble metal nanomaterials (NMNs) to address challenging issues in the environment has attracted recent interest in the community. In general, the use of NMNs for environmental applications is highly dependent on the physical and chemical properties of NMNs. Such properties can be readily controlled by tailoring the attributes of NMNs, including their size, shape, composition, and surface. In this feature article, we discuss recent progress in the rational design and engineering of NMNs with particular focus on their applications in the field of environmental sensing and catalysis. The development of functional NMNs for environmental applications is highly interdisciplinary, which requires concerted efforts from the communities of materials science, chemistry, engineering, and environmental science.

Direct synthesis of pure single-crystalline Magnéli phase Ti8O15 nanowires as conductive carbon-free materials for electrocatalysis

The Magnéli phase Ti8O15 nanowires (NWs) have been grown directly on a Ti substrate by a facile one-step evaporation-deposition synthesis method under a hydrogen atmosphere. The Ti8O15 NWs exhibit an outstanding electrical conductivity at room temperature. The electrical conductivity of a single Ti8O15 nanowire is 20.6 S cm(-1) at 300 K. Theoretical calculations manifest that the existence of a large number of oxygen vacancies changes the band structure, resulting in the reduction of the electronic resistance. The Magnéli phase Ti8O15 nanowires have been used as conductive carbon-free supports to load Pt nanoparticles for direct methanol oxidation reaction (MOR). The Pt/Ti8O15 NWs show an enhanced activity and extremely high durability compared with commercial Pt/C catalysts.

Environmental applications of graphene-based nanomaterials

A critical assessment of recent developments in environmental applications of graphene and graphene-based materials.

Nanoparticles of Pt loaded on a vertically aligned TiO2 nanotube bed: synthesis and evaluation of electrocatalytic activity

Pt nano particle loaded TiO₂ nanotube (TiNT) electrode with excellent electrocatalytic activity was synthesized via seed mediated hydrothermal reduction method on self-aligned TiNT bed.